Re: Wasn't v. Helmholtz right? (BM/neural tuning)

[Andrew Bell <bellring@xxxxxxxxxxxxxxxx>]

Dear Enrique and List:

It is clear that this data (like similar data over previous years)
demonstrates that the BM and neural curves are equally sharply tuned. The
puzzling question then naturally arises - and it is a question that has been
vexing hearing science for quite some time (a century or more) - how could
the BM (or any passive cochlea structure) be so sharply tuned when it is
essentially a slack membrane, or conjoined fibres, immersed in fluid? Such a
structure would have a very low Q.

So if we assume that 'intermediate' structures merely amplify the BM
response, we end up with something with a similarly low Q. As Gold
suggested, some positive feedback is needed to sharpen the response.

I have suggested a mechanism involving the OHC and tectorial membrane that
provides high Q in a fluid environment. Incidentally, the BM picks up this
vibration. However, the BM is not the primary tuned element of the ear; it
is an accessory structure designed to absorb excess energy.



Andrew.


-----Original Message-----
From: AUDITORY Research in Auditory Perception
[mailto:AUDITORY@LISTS.MCGILL.CA]On Behalf Of Enrique A. Lopez-Poveda
Sent: Tuesday, 27 June 2000 12:38
To: AUDITORY@LISTS.MCGILL.CA
Subject: Re: Wasn't v. Helmholtz right? (BM/neural tuning)


Andrew,

I take your point and I agree with your comment that Narayan et al. could
have made the curves to match at their base.  In that case, neural
thresholds would be lower than the BM threshold.  However, even if you did
that, their data show that BM response is as sharply tuned as AN response.
The bandwidths of their tuning curves are comparable at the tip, even
though their thresholds may be different.  Assuming that the BM and AN
tuning curves are made to match at their tails, one could then argue that
the role of intermediate structures (e.g., OHC, IHC, etc) could be only to
"amplify" the BM response, but NOT to sharpen the tuning of the system.
Any comments on this?

-- Enrique